1. Field of the Invention
The present invention relates to methods and apparatus for tissue engineering using a bioreactor system. More particularly, the invention relates to producing and collecting blood cells in a bioreactor system environment that re-creates the pressure differential between the tissue interstitial pressure and the outflow capillary and venular pressure.
2. Description of the Related Art
Shortages of red blood cells for transfusion can delay elective surgeries, and even affect disposition of trauma center triage. Since originally conceptualized by Trentin (1970), the blood-forming microenvironment has become understood as the necessary tissue niche inductive of blood cell production by blood stem cells. Tissue engineering offers a potential solution to the blood cell shortage problem by taking advantage of progenitor or stem cells located in bone marrow. Stem cells in the marrow of the body's longest bones are continuously at work to meet the body's varying demand for billions of new blood cells a day. Tissue engineering techniques can potentially be used to produce red blood cells, white blood cells, and/or blood platelets, through sampling of bone marrow stroma, isolating of progenitor cells, multiplying of the cells until a sufficient cell number is obtained, and seeding of the cells onto scaffolds. By cultivating this tissue in a bioreactor system, it is possible to provide local environmental conditions that will encourage the cells to differentiate in a particular direction (i.e., differentiate into blood cells). Additionally, stem or progenitor cells for some cell or tissue lineages, including hematopoietic, can be collected from peripheral blood by apheresis with minimal discomfort to the blood donor compared to bone marrow harvest. While tissue engineering is potentially a very beneficial solution to blood cell shortages, mastering tissue-engineering techniques that will successfully result in production of red blood cells is a challenge that is still far from being resolved.
One problem is creating the appropriate design of bioreactor systems for blood cell production. The rational design of bioreactor systems for blood cell production is being discussed in current biomedical scientific articles (Cabrita et al., 2003; Noll et al., 2002; and Nielsen, 1999). Three-dimensional systems for extracorporeal blood cell production have been reported on nylon mesh (Naughton et al., 1991), in hollow fibers (Rice et al., 1994), and on porous microspheres (Mantalaris et al., 1998), as well as in sterilized spongy (marrow cavity) bone (Januszewski et al, 2003). However, these bioreactor systems do not allow red blood cells to be safely and economically cultivated extracorporeally. These bioreactors start with components (e.g., hollow fibers or microspheres) to build upward to cultivate tissue that is engineered to produce blood cells, as opposed to starting at the bone marrow tissue level and deconstructing the tissue into components that can be used to repopulate a three-dimensional bone marrow tissue extracellular matrix.
Current bioreactor systems fail to provide an appropriate environment for production of blood cells. For example, there is currently no effective tissue-cultivation bioreactor system that duplicates the marrow tissue conditions at the tissue level. In most animal tissues, the interstitial fluid outflow of the extravascular space is into capillaries of the arteriovenous and lymphatic vascular systems, and mostly to the former.
In most animal tissues, the interstitial fluid outflow of the extravascular space of tissues, including marrow tissue, is into capillaries of the arteriovenous and in some cases to the lymphatic vascular systems. The capillary network of the arteriovenous system connects to venules or venioles (which are tributaries of the low pressure venous intravascular space), and there is a pulsing or oscillating component of the low-pressure hydrodynamics in the venous intravascular pressure. The current bioreactors fail to recognize or mimic this pressure differential and fail to create realistic tissue conditions as they exist in animal tissues.
Therefore, there is a need for a new approach to bioreactor technology that mimics the realistic tissue conditions existing in animal tissues and that creates a microenvironment that results from interactions of bone marrow-derived connective tissue cells and blood stem cells that are repopulated on and interact within a biochemically complex, three-dimensional bone marrow tissue extracellular matrix. The present invention addresses these and other deficiencies of the prior art as described more fully below.